The present invention relates generally to orthopedic implants for use in a joint fusion (including fibrous union or even non-union), or as a post for use in a dental procedure. In particular, the implant of the present invention relates to an interphalangeal fusion implant which provides for a stable relationship between two phalanges, such as the proximal phalange and the intermediate phalange, which exists at the proximal interphalangeal joint. Specifically, this implant provides enhanced fixation strength for PIPJ fusion by providing a large cancellous screw thread in the middle phalanx and a longer barbed segment in the proximal phalanx.
Digital deformities of the fingers and toes are some of the most common conditions encountered by small bone specialists. Patients with digital deformities often experience significant pain from structural abnormalitis. Some of these abnormalities are acquired, caused by traumatic injuries, neuromuscular pathologies, systemic diseases, or mechanical problems secondary to extrinsic pressures. Examples of such deformities are popularly known as mallet finger, jersey finger, coach's finger, hammertoe, mallet toe, and claw toe, as well as a host of others, indicative of several different pathologies.
A particular condition, which is suitable for correction using the implant of the present invention, is hammertoe, and related muscular imbalances of the toes. Hammertoes are a contracture of the toes, which result from a muscle imbalance between the tendons on the top and the tendons on the bottom of the toe. Frequently, hammertoes are accompanied by painful corns and callouses. Hammertoe is generally described in the medical literature as an acquired disorder, typically characterized by hyperextension of the metatarsophalangeal joint (MTPJ), hyperflexion of the proximal interphalangeal joint (PIPJ), and hyperextension of the distal interphalangeal joint (DIPJ). In some cases, surgical intervention is the best chance for successfully realigning the toe and for alleviating the pain that accompanies the disorder.
In order to prevent recurrence of the deformity and ensure the success of the surgical procedure, a proximal interphalangeal (PIP) joint arthrodesis is typically performed. The most commonly used hammertoe procedure is that which was described by Post in 1895 and is referred to today as the Post Arthroplasty or Post Procedure. The Post Procedure involves resecting (removing) the knuckle of the toe at the level of the proximal interphalangeal joint (PIPJ). This joint is the joint closest to the point where the toe attaches to the foot. Typically the Post Procedure will be performed in conjunction with a tendon release on the top (extensor surface) of the foot. The combination of these two procedures results in a toe that will lay flatter avoiding direct pressure from the shoe. In the case of a mallet toe or claw toe, the Post procedure may be performed with or without the tendon lengthening. The “end-to-end ” or “peg-in-hole” techniques are the most commonly used procedures to resect the PIPJ. The PIPJ is aligned with the rest of the toe in a corrected anatomical position and maintained in place by the use of a 0.045 inch −0.062 inch Kirschner wire (K-wire) driven across the joint. Initially, the wire is placed from the PIPJ through the tip of the toe. It is then driven in retrograde fashion into the proximal phalanx. The exposed wire exiting the toe is bent to an angle greater than 90 degrees, and the bent portion is cut at 1 cm from the bend. At the conclusion of the surgical procedure, a small compressive dressing is placed around the toe, with a Jones compression splint being used for three to four weeks to protect the pin and the toe in order to maintain correction. The K-wire and the Jones splint are generally removed three weeks after surgery.
Similar procedures may be followed to create arthrodesis of the distal interphalangeal joint (DIP) of the toe or for arthrodesis performed in the finger to correct digital abnormalities of the hand. In procedures that involve the use of an implant such as a prior art pin, an incision is made in the top of the toe to expose the affected joint. Subsequently, the surgeon releases the dorsal capsule and extensors tendons at the level of the metatarsal phalangeal joint. Then the extensor tendon is resected and the PIPJ ligaments are released from the medial and lateral sides of the PIPJ. The proximal phalangeal head is resected with a pair of bone nippers, and an implant, such as a pin or a nitinol implant is inserted starting in the proximal bone between the phalanges and the wound is closed.
Although this type of surgical procedure has alleviated the discomfort of hammertoe and other abnormalities of the toe and finger joints for prior patients, there are disadvantages that can surface from the use of the prior art procedures and devices, including swelling, infection at the wound cite, rotation of the affected phalanges, surgical difficulties resulting from overly fussy device material or device, and misalignments resulting from patient non-compliance. In contrast, the present invention assures that the phalanges will remain more securely in the desired relationship for the fusion of the bones, and further creates greater stability at an immediate post-operative stage ensuring greater chances of success regardless of the post-operative compliance of the patient.
The present implant is easier to insert than the prior art implants. It is a single unit integral structure (as used herein “integral” means that it is manufactured out of a material as a single piece, and does not comprise an assembly of components such as two pieces that snap, lock or thread together.) Thus, it does not require the surgeon to assemble components as part of the surgery, but rather allows the surgeon to implant a first end in a first bone segment and to anchor a second bone segment on an opposing second end, for example, in retrograde fashion. It does not require the temperature change that is required in a nitinol implant. Several of the embodiments of the present implant are radially symmetrical or functionally radially symmetrical about the longitudinal axis (i.e., while not radially symmetrical, the placement and sizing of the barbs functions as a radially symmetrical set of barbs would in a cylindrical hole). This eliminates the requirement that the implant is implanted at a specific radial orientation, which may be difficult to achieve or monitor. It also provides more options for the operating surgeon. At his or her discretion, it allows for temporary fixation at the metatarsal, which assists the surgeon by providing a k-wire to guide the implant into the proper position. This feature provides the surgeon with the option of maintaining the wire in the implant to eliminate the common complication of a raised toe from the metatarsal. The pin may subsequently be withdrawn (during that surgery or in a later office visit) without jeopardizing the integrity of the implant if infection due to percutaneous pin is a concern.